Rob...I noticed a posting on another collector website with a link to an article on this very subject. Looks like the coin is going to stay in the UK. Latest News
Like Rob, I also had not seen the advertisement, but I noticed the same or a similar advert on page 41 of the latest (February) issue of Coin News. He also has a 1642 triple unite and a gold 1797 Cartwheel penny.
This may be somewhat off-topic, but I have heard that a similar problem exists in the area of 19th century Maundy and currency issues whereas some Maundy issues are being offered as their rarer currency counterparts.
I actually tuned in on time -- but only because I wasn't certain of the time difference between here and the UK. Chris -- in addition to the call-ins -- have you ever thought of interviewing other dealers and/or collectors on the show?
Wybrit -- I don't recall any customs duty being charged in the other direction (UK to US). Do you know if this is just an oversight or is US customs supposed to charge a duty?
All of the coins being offered by this seller appear to be unnaturually lustrous. On the farthings he is selling he notes that "These coins are offered to you in 'Very Fine' Condition and still retain their original lustre". Perhaps he works for one of the US grading services?